U.S. patent number 4,627,844 [Application Number 06/792,904] was granted by the patent office on 1986-12-09 for tri-layer tubing.
This patent grant is currently assigned to High Voltage Engineering Corporation. Invention is credited to Jerry A. Schmitt.
United States Patent |
4,627,844 |
Schmitt |
December 9, 1986 |
Tri-layer tubing
Abstract
A coextruded tri-layered medical-surgical tubing for the
administration of common medicines such as insulin and
nitroglycerin solutions is disclosed. Improved flexibility and
uniformity and increased peel strength are obtained by interposing
a layer of an ethylene-vinyl acetate copolymer between an outer
layer of polyvinyl chloride and a core layer of low-density
polyethylene. The composite tubing exhibits excellent fluid flow
characteristics and is readily employed in the transportation of
intravenous fluids and the like without absorbtion or contamination
difficulties.
Inventors: |
Schmitt; Jerry A. (Lionville,
PA) |
Assignee: |
High Voltage Engineering
Corporation (Burlington, MA)
|
Family
ID: |
25158425 |
Appl.
No.: |
06/792,904 |
Filed: |
October 30, 1985 |
Current U.S.
Class: |
604/264; 138/137;
428/36.6; 604/523 |
Current CPC
Class: |
A61L
29/041 (20130101); A61L 29/085 (20130101); A61M
25/0045 (20130101); A61L 29/041 (20130101); C08L
31/04 (20130101); A61L 29/085 (20130101); C08L
27/06 (20130101); A61L 29/041 (20130101); C08L
23/06 (20130101); A61L 29/041 (20130101); C08L
31/04 (20130101); A61L 29/085 (20130101); C08L
27/06 (20130101); Y10T 428/1379 (20150115) |
Current International
Class: |
A61L
29/04 (20060101); A61M 25/00 (20060101); A61L
29/08 (20060101); A61L 29/00 (20060101); A61M
005/325 (); A61M 025/001 () |
Field of
Search: |
;604/264,86,280-284,266
;138/137,140,103 ;428/36 ;264/173,209.1 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
0144629 |
|
Jun 1985 |
|
EP |
|
0139757 |
|
Oct 1981 |
|
JP |
|
0075553 |
|
May 1983 |
|
JP |
|
0129137 |
|
Jul 1984 |
|
JP |
|
Primary Examiner: Rosenbaum; C. Fred
Assistant Examiner: Smith, Jr.; Jerome R.
Attorney, Agent or Firm: Nields; Henry C.
Claims
I claim:
1. A coextruded tri-layered medical-surgical tubing for the
administration of common medicines such as insulin and
nitroglycerin solutions, said tubing comprising an outer layer of
polyvinyl chloride, a core layer of low-density polyethylene, and
an intermediate layer of an ethylene-vinyl acetate copolymer
interposed between said outer layer and said core layer.
2. A tubing in accordance with claim 1 wherein said outer layer
includes trioctyl trimellitate as a plasticizer.
3. A tubing in accordance with claim 2 wherein the thickness of
said intermediate layer is in the range 0.0007 to 0.0015 inches and
the thickness of said core layer is in the range 0.0025 to 0.004
inches.
4. A tubing in accordance with claim 2 wherein said intermediate
layer has a vinyl acetate content of 28 percent by weight of said
copolymer.
5. A method of making tri-layered medical-surgical tubing for the
administration of common medicines such as insulin and
nitroglycerin solutions comprising simultaneously and coaxially
extruding an outer layer of polyvinyl chloride containing a
plasticizing amount of trioctyl trimellitate, a core layer of
low-density polyethylene, and an intermediate layer of an
ethylene-vinyl acetate copolymer in such a manner that upon
extrusion said intermediate layer is intimately bonded to said
outer layer and to said core layer.
Description
BACKGROUND OF THE INVENTION
Plastic tubings are extensively employed in the medical field,
particularly for patient analysis and treatment procedures. Various
plastics and combinations thereof are used, depending upon the
specific properties the intended application demands. The selection
of desired plastic materials is further limited by the use of the
tubing in the in vivo treatment of human patients, as the tubing
may be used in the administration of intravenous fluids or itself
may be introduced into the body. Thus numerous factors must be
considered in ascertaining which materials to choose.
Polyvinyl chloride (PVC) is the standard material used, made with
suitable plasticizers necessary to enhance flexibility and other
properties. However, such plasticizers or similar additives have a
tendency to migrate, causing hazardous contamination with the fluid
being administered. The contamination becomes more serious where
the fluid is introduced into the body, as contamination of the
blood may result, Moreover, plasticized PVC tubings have been shown
to absorb nitroglycerin and insulin, and are thus unsatisfactory
for the administration of these medicines. Much effort has been
directed towards finding an alternative that does not suffer from
the limitations of the plasticized PVC tubing. Polyurethane has
been used, as in U.S. Pat. No. 4,211,741 to Ostoich. Because it is
a relatively soft, flexible plastic even without additives,
additives are not necessary, their absence thereby minimizing
migration possibilities. In addition, it exhibits good fluid flow
characteristics. However, the high cost of polyurethane has limited
its use to only extraordinary applications. Some grades of
ethylene-vinyl acetate copolymer (EVA) are currently being used as
an outer layer, together with low-density polyethylene (LDPE) as an
inner layer. Although this composite exhibits excellent peel
strength, it lacks flexibility, clarity, and is easily scuffed or
roughened. In addition, it cannot be solvent bonded. Since the
tubing is the connecting link between a reservoir of fluid
(nitroglycerin, insulin, etc.) and the patient, the method of
assembly is an important consideration. Where, as here, solvent
bonding cannot be utilized, an expensive, less reliable mechanical
means of assembly are required, whereby a PVC layer must be
pressure fit over the EVA-LDPE tubing to utilize the solvent
bondable characteristics of PVC. For these reasons, the EVA-LDPE
product has proven to be unsatisfactory.
The ideal product would have a thick, flexible outer layer
comprised of PVC and a thin layer of LDPE, thus exploiting their
respective advantages through strategic placement. Under normal
extrusion conditions of temperature and pressure, however, PVC and
LDPE will not bond together. Consequently, undesirable layer
separation occurs. A third or "tie layer" is therefore required
which will bond to both the outer PVC layer and the inner LDPE
layer.
It is therefore, an object of the present invention to provide a
coextruded, tri-layered, solvent bondable, soft, flexible plastic
tubing which can be utilized in the administration of nitroglycerin
and insulin.
Other and related objects and advantages will become evident from
the following specification and claims.
SUMMARY OF THE INVENTION
The present invention is particularly directed toward a coextruded,
tri-layered medical tubing employed in the administration of
insulin and nitroglycerin. The outer layer of the tubing is
flexible PVC made with trioctyl trimellitate plasticizer (TOTM).
The middle "tie layer" is comprised of EVA, and the inner layer of
LDPE. The TOTM-based PVC, developed for blood contact applications,
has exhibited exceptional bond strength with the EVA resin middle
layer, thereby eliminating any separation problems previously
encountered. This combination of materials maintains the structural
integrity of the layer tubing construction even after a gas
sterilization cycle, and a fortiori, where an irradiation
sterilization process is used, the strength of the bonds are
actually enhanced.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The invention can best be understood from the following detailed
description of a preferred embodiment thereof, having reference to
the accompanying drawing, in which:
FIG. 1 is an isometric view of a tri-layered tubing of the
invention with the outer layer and middle layer broken away in
order to show the construction, and
FIG. 2 is an enlarged cross-section of the tri-layered tubing of
the invention comprising an outer layer 1 of flexible PVC made with
trioctyl trimellitate plasticizer (TOTM), a middle layer 2 of EVA,
and an inner layer 3 of LDPE.
The respective thickness of each layer of tubing can be controlled
by the extrusion tooling utilized, such as the "Tri Die" extrusion
apparatus manufactured by the Genca Division of General Cable
Company, Clearwater, Fla. Use of such sophisticated tooling results
in concentric, uniform thickness, characteristics necessary for the
high performance demanded by medical applications. Together with
high grade plastics, the use of superior equipment will also aid in
maintaining the possibility of voids, skips or cracks forming
between layers, insuring that the medicines will not contact the
PVC layer. General Cable's equipment is also desirable for its ease
of assembly and operation, durability, flexibility, and
sophisticated design to control flow. Indeed, use of such equipment
allows control of each of the three layers of +0.0002 inches.
The thickness of each layer depends on the overall specifications
requested by the user. To obtain the optimum balance of adhesion
and clarity, an EVA layer ranging from 0.0007 to 0.0015 inches is
preferred. The optimum thickness of the LDPE layer is from 0.0025
to 0.004 inches, which insures a continuous coating on the inside
diameter while maintaining a balance of flexibility, adhesion and
clarity in the final product. The preferred vinyl acetate content
of the EVA is 28%, which allows for maximum flexibility without
losing the desired extrusion characteristics.
The following example if given for illustration of the peel
strength of various combinations of materials and aging
conditions:
EXAMPLE I
To determine acceptable levels of adhesion of the three layers, a
peel test was developed and performed on the extruded tubing. The
procedure used is as follows:
1. Using a holding fixture, cut lengthwise and 8-inch length of
tubing with a razor blade.
2. Using a sharp instrument such as a razor blade, scrape the inner
two layers (polyolefin layer) away from the flexible PVC outer
layer.
3. Peel the exposed end of the polyolefin layer away from the
flexible PVC layer for a distance of 1-1.5 inches.
4. Place a small mark on the outside of the flexible PVC layer,
about 2.5-3 inches from the end that the polyolefin layer has been
placed.
5. Place the flexible PVC end in the upper jaws of a tensile
testing machine (Instron), and place the polyolefin end in the
lower jaws.
6. Start the machine. Initial jaw separation=1"; jaw separation
speed=20" per minute.
7. Mark the recording chart when the peel interface reaches the
mark on the outside of the flexible PVC. Record this number as the
force required to separate the layer at this point.
8. Having set the machine to stop at a predetermined distance that
is less than the length of the specimen, remove the specimen from
the jaws after the machine has returned to the start position.
Measure the peel surface length of the PVC layer and the length of
the polyolefin layer and record these values.
9. Measure the width of the specimen at the previously applied mark
on the flexible PVC layer. A machinist's microcope is helpful.
10. Calculate the "peel strength" of the layers by dividing the
force at the mark (recorded in step 7) by the width at the mark
(recorded in step 9). This value is the peel strength of the
flexible PVC layer to the polyolefin layer, expressed as pounds per
inch of width (P.I.W.).
The results of representative experiments using the foregoing
procedure are shown in Table 1. Table 1 indicates that tri-layer
tubing utilizing dioctyl phthalate (DOP) plastizer based PVC in the
outer layer has a significant reduction in peel strength after oven
aging for twelve hours @ 135.degree. F.(135.degree. F. was selected
as a typical temperature for a gas sterilization cycle.) Tri-layer
tubing utilizing trioctyl trimellitate (TOTM) plasticizer based PVC
in the outer layer suffers no loss of peel strength under the same
conditions.
Further testing of the DOP-PVC tri-layer tubing and the TOTM-PVC
tri-layer tubing for sixty hours @ 140.degree. F. resulted in the
DOP-PVC tri-layer tubing losing essentially all of its peel
strength. The TOTM-PVC tri-layer tubing retains a much higher
percentage of its peel strength under these exceptional
conditions.
TABLE 1
__________________________________________________________________________
PEEL TEST RESULTS
__________________________________________________________________________
TIME @ TEMPERATURE 24 HRS. @ 78.degree. F. 12 HRS. @ 135.degree. F.
60 HRS. @ 140.degree. F. OUTER LAYER/MIDDLE LAYER/ PEEL
STRENGTH.sub.1 PEEL STRENGTH.sub.1 PEEL STRENGTH.sub.1 INNER LAYER
DOP-PVC/EVA/LDPE 3.2 1.9 0.01 TOTM-PVC/EVA/LDPE 3.6 3.6 0.79
__________________________________________________________________________
.sub.1 Units are pounds per inches of width as outlined in example
1.
Having thus described the principles of the invention, together
with an illustrative embodiment thereof, it is to be understood
that although specific terms are employed they are used in a
generic and descriptive sense, and not for purposes of limitation,
the scope of the invention being set forth in the following
claims:
* * * * *